In order to meet the ever-increasing demands for greater levels of integration with fewer off-chip components, radio receivers are increasingly moving to architectures such as low IF. A low-IF receiver down converts a desired spectrum directly from RF to some very low-IF (typically <few 10s of MHz). Low-IF receivers can be highly integrated, since filtering can be done on-chip while maintaining high performance. Further, low IF is a powerful measure to fight spurious emissions in LTE-CA/-A and DR-DSDS capable transceivers. In addition, the down converted spectrum is at a low enough frequency that it can be easily sampled by low-power analog-to-digital converters (ADC), and is thus also known as digital IF. The spectrum may then be converted to baseband using digital signal processing (DSP). In some cases, the down converted spectrum is in the same frequency range as the baseband. However, one feature of this type of receiver is that a blocker signal which is an unwanted signal at a mirror image frequency of the wanted signal frequency is always relatively close to the wanted signal and is often arranged to be one of the adjacent channels. As a result, separation of the wanted signal from the blocker signal by filtering at RF is impracticable.
One characteristic of a low IF receiver is that it relies on good internal matching in its quadrature architecture to achieve high levels of adjacent channel rejection. That is, if there is an imbalance in the amplitude and phase between the I and Q channels, an extremely strong signal at the mirror image frequency will cause interference to the desired signal in the IF, if the desired signal is too weak, for example, in reference sensitivity cases or high modulation schemes like 64 QA+. This means that in situations where the blocker channel (i.e., the adjacent channel) is large relative to the wanted channel, some of the interferer in the blocker channel can find its way into the wanted signal spectrum. This results in a degradation in bit error rates at the output of the demodulator.